Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 4 3 2004 10.5194/acpd-4-3535-2004 http://www.atmos-chem-phys-discuss.net/4/3535/2004/ http://www.atmos-chem-phys-discuss.net/4/3535/2004/acpd-4-3535-2004.html http://www.atmos-chem-phys-discuss.net/4/3535/2004/acpd-4-3535-2004.pdf 3535 3563 2004-06-25 Atmospheric particle formation events at Värriö measurement station in Finnish Lapland 1998–2002 H. Vehkamäki hanna.vehkamaki@helsinki.fi M. Dal Maso T. Hussein R. Flanagan A. Hyvärinen J. Lauros J. Merikanto P. Mönkkönen M. Pihlatie K. Salminen L. Sogacheva T. Thum T. Ruuskanen P. Keronen P. P. Aalto P. Hari K. E. J. Lehtinen Ü. Rannik M. Kulmala Department of Physical Sciences, P.O. Box 64, University of Helsinki, 00014 Helsinki, Finland Finnish Meteorological Institute, P.O Box 503, 00101 Helsinki, Finland Department of Forest Ecology, P.O. Box 27, University of Helsinki, 00014 Helsinki, Finland We have identified 147 clear 8 nm diameter particle formation events at the SMEAR I station in Värriö, northern Finland during calendar years 1998–2002. The events have been classified in detail according to the particle formation rate, growth rate, event starting time, different gas phase species concentrations and pre-existing particle concentrations as well as various meteorological conditions. Most of the events occurred during the spring months between March and May, suggesting that increasing biological activity might produce the precursor gases for particle formation. The apparent 8 nm particle formation rates were around 0.1/cm³s, and they were uncorrelated with growth rates that vary between 0.5 and 10 nm/h. The air masses, which had clearly elevated sulphur dioxide concentrations above 1.6 ppb came, as expected, from the direction of Nikel and Monschegorsk smelteries. Only 15 formation events can be explained by the pollution plume from these sources.